Avoid printing garbled error message from image.el

* lisp/image.el (image--get-imagemagick-and-warn): Don't use
apostrophe in the error message, as that message is shown from a
unibyte buffer, and will run afoul of the default style of showing
quote characters.  (Bug#30405)

lisp/image.el

@@ -977,7 +977,7 @@ default is 20%."
 
 (defun image--get-imagemagick-and-warn ()
   (unless (fboundp 'imagemagick-types)
-    (error "Can't rescale images without ImageMagick support"))
+    (error "Cannot rescale images without ImageMagick support"))
   (let ((image (image--get-image)))
     (image-flush image)
     (plist-put (cdr image) :type 'imagemagick)